Method of and device for establishing the correct lead required for firing a projectile at a moving target



Ap 1970 E. w. SUNDSTROM METHOD OF AND DEVICE FUR ESTABLISHING THECORRECT LEAD REQUIRED FOR FIRING A PROJECTILE AT A MOVING TARGET FiledAug. 30, 1966 2 Sheets-Sheet 1 INVENTOR.

ERIK w/wzm sawpsmbkv April 28, 1970 E. w. SUNDSTROM 3,508,335

METHOD OF AND DEVICE FOR ESTABLISHING THE CORRECT LEAD REQUIRED FORFIRING A PROJECTILE AT A MOVING TARGET Filed Aug. 30, 1966 2Sheets-Sheet 2 I 48 a) R V 4.9 fia) r FIG. 3

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INVENTOR.

ERIK W/LHELM savasredm BY n A r To/EWE r:

United States Patent US. Cl. 33-49 Claims ABSTRACT OF THE DISCLOSUREInitially a sight line and gun barrel are moved both at the same angularvelocity relative to a moving target until the sight line and the barrelare aimed at the target. An additional velocity component angularlyopposite to the concurrent movement of the barrel is then applied to thesight line for a selected interval of time while the barrel and thesight line are being moved to aim the sight line at the target duringthis interval of time. The additional oppositely directed velocitycomponent is se ected so that the angular velocity of the line of sightis of the angular velocity of the barrel during the selected interval oftime, at being a constant. At the end of the time interval the relativemovement of the sight line and the gun barrel is stopped but aiming thesight line at the target is continued at an angular velocity equal tothat of the barrel.

The present invention relates to a method of achieving a correct leadwhen firing projectiles against a moving target, and a device forcarrying out the method. This method is particularly well suited forfirearms mounted on track-laying vehicles, and can also be used withadvantage on track-laying vehicles in which the weapon has a fixedmounting in the vehicle and it is thus aimed by steering the wholevehicle.

BACKGROUND It is previously known, for obtaining a lead when firingprojectiles against moving targets, to allow the reticule in the sightto be given a momentary displacement, the size of which has beendependent upon the speed of the target and the time of flight of thefired projectile. However, such a means of achieving an appropriate leadwhen firing projectiles against a moving target involves considerabledisadvantages, for instance in that the aiming of the Weapon is madediflicult by the sudden displacement of the reticule, and that in orderto be able to achieve a correct lead, it is necessary to be able toobtain satisfactory data, rapidly, for the speed of the target and thetime of flight of the projectile.

THE INVENTION Through the present invention, the above-mentioneddisadvantages have been eliminated, and it has become possible toachieve the lead without any sudden displacement of the reticule, andthe only setting required, apart from the actual tracking of the target,is the one that is based upon the calculated range to the target.

SUMMARY OF THE INVENTION The aforepointed out object, and other objectswhich will be pointed out hereinafter are obtained by establishing thecorrect lead for firing a projectile from a gun barrel at a movingtarget by initially moving the sight line and the gun barrel both at thesame angular velocity relative to the target until the sight line istracking the target and the gun barrel is aimed at the target. The sightline is then driven angularly and oppositely relative to the gun barrelat a constant times the angular velocity of the barrel for apredetermined time interval of time or times the time 1 while seeking tocontinue tracking the target, a being a constant and t the time offlight of the projectile from the barrel to the target. At the end ofthis time interval the relative movement of the sight line and the gunbarrel is stopped but aiming the line of sight and the barrel at thetarget is continued.

The method of the invention may be carried out by an apparatus whichcomprises a sighting assembly including a carrier bearing a reticule.This carrier is so mounted that the reticule can be vertically andtransversely displaced alternatively with or relative to the gun barrelwhich, in turn, can be elevated and depressed. A relative movement isimparted to the carrier proportional to and in opposition to the angularmovement of the gun barrel. Reduction of said relative movement reducesthe angular velocity of the line of sight in relation to that of the gunbarrel by a factor where a is a constant. The relative movement isimparted to the carrier by transmission means which are operated byactuating means coupled to the transmission means for a set interval oftime and uncoupled therefrom at the end of this interval. Uncoupling ofthe transmission means frees the carrier and thus the reticule to moveat the angular velocity of the gun barrel.

DETAILED DESCRIPTION OF AN EMBODIMENT The invention will now bedescribed in more detail, with reference to an embodiment shown in theattached figures. FIG. 1 shows, schematically and in perspective, atrack-laying vehicle, where a gun mounted in a rotatable turret has beenprovided with a device according to the present invention. In FIG. 2 thedesign of the device indicated in FIG. 1 is shown, also schematicallyand in perspective, in more detail. FIG. 3 contains a diagram in whichcertain angular velocities have been plotted as a function of the time,and in FIG. 4 finally, a diagram is shown of the corresponding angularpositions as a function of the time.

The track-laying vehicle shown in FIG. 1 is provided with a rotatableturret 2, in which the gun barrel 3 is mounted. The movement of theturret 2 is provided for by a motor 4, which is fixed to the turret anddrives a gear wheel 5, which is in mesh with a gear ring 6 rotatablyfixed to the vehicle 1. In the corresponding way, the elevating movementof the barrel 3 is controlled by the motor 7 which is fixed to theturret 2, and which via the gear wheel 8 engages in a gear segment 9,which is fixed to the barrel. The movements of the motors 4 and 7 aretransmitted to a lead generator 10A supported by a sight assembly 10supported by the turret 2 for movement in unison with the gun barrel, bymeans of flexible shafts 1.1 and 12. There is also a cable 13 connectedto the lead generator 10A and to a timer 14, which, in turn, via thecable 15 is connected with the pedal 16, which can be actuated by thegunner when aiming the barrel 3.

The further details of the construction of the lead generator 10A areshown in FIG. 2. In the sight 10, with its eyepiece 17, there is a glassplate 18, which has thereon a reticule and constitutes a carriertherefor. This glass plate 18 can be displaced in its own plane, bothhorizontally and vertically. The horizontal displacement is achieved bymeans of the gear rack 19 which via the sliding holder 20 laterallypositions the strip 21 which is fixed to the glass plate 18. In acorresponding way, the vertical displacement of the glass plate 18 isachieved by means of the gear rack 22, which via the sliding holder 23laterally positions the strip 24 fixed to the glass plate 18. Themovement of the gear rack 19 is achieved by means of the gear wheel 25,which is fixed to the shaft 26. On this shaft 26 also, the gear wheel 27and the knob 28 are fixed. There is also a gear wheel 29 arranged, whichis permanently in mesh with the gear wheel 27, which gear wheel 29, bymeans of a clutch, can be actuated by the flexible shaft 11 from themotor 4. This clutch consists of a disk 30, which can be displaced onthe shaft 12, which by means of keys which can slide in grooves made inthe shaft 11, always participates in the rotation of the shaft 11. Thedisk 30 is provided with a number of friction linings 31, which underthe influence of the electromagnet 32 can be made to bear against thegear wheel 29. h electromagnet 32 receives its current through thecables 33 and 34, which via the cable 13 are connected with the timer14.

In the corresponding way, the gear rack 22 can be actuated by the gearwheel 35, which is fixed to the shaft 36 on which also the gear weel 37and the knob 38 are fixed. The gear wheel 39 can be actuated, by meansof the clutch consisting of the displaceable disk 40 with the linings 41and the electromagnet 42, by the flexible shaft 12, which is connectedwith the motor 7. The electromagnet 42 is connected with the timer 14via the cables 43 and 44 and 13.

The timer 14 is provided with a pointer 45, which can be set atdifferent values, and is connected via the cable 15 with a switch 46,which can be actuated by the pedal 16.

The device described above functions in the following way. When aimingat a moving target, the pointer 45 of the timer is set so that the timer14 gives a time impulse which is proportional to the time of flight(t,,) of a fired projectile from the barrel to the target. The time a-tset on the timer l4 naturally depends upon the value which is electedfor the constant a as well as on the distance to the target and thevelocity of the fired projectile. When a suitable value of the constanta has been chosen (which should appropriately be between 0.5 and 3) andthe velocity of the projectile estimated, only the distance from thebarrel to the target need be determined. Thus, the scale for the settingof the pointer 45 on the timer 14 can be graduated directly in saiddistance.

When the timer 14 has been set at an appropriate range, and after thereticule and therewith also the barrel have been aimed directly at thetarget, by depressing the pedal 16, through which the switch 46 isswitched on, the gunner can start the timer 14. Current pulses are thenemitted from this timer through the cables 13, 33, 34, 43 and 44, to thewindings of the electromagnets 32 and 42. The duration of this series ofcurrent pulses depends upon the setting of the pointer 45, and is to beat times the time t of flight of the projectile from the barrel to thetarget, i.e. Ot'l During the period of time (at-t for which theelectromagnets 32 and 42 receive current from the timer 14, the disks 30and 40 Will be displaced in the direction towards the gear wheels 29 and39, respectively, and under the influence of the friction linings 31 and41, respectively, these gear wheels 29 and 39 will have the same speedas the shafts 11 and 12, respectively, during said period of time (ot'lThis movement of the gear wheels 29 and 39 is transmitted via the gearwheels 27 and 37 to the shafts 26 and 36, respectively, and from therevia the gear Wheels 25 and 35 to the gear racks 19 and 22, respectively.

Due to the impulse emitted from the timer 14, the glass plate 18 withits reticule will therefore during the period of time (ix-t have adisplacement depending upon the movements of the shafts 11 and 12,respectively. During the time interval tit-t the gun barrel is to movethrough the angle co et-t traveled by the target plus the angle w twhich is the proper lead angle. Therefore should be the average angularspeed of the barrel relative to the craft during that interval. If thesight line is made to track the target still moving at w during thatinterval, its average angular speed realtive to the craft will be mwhich from the above is a rx/ 1+a) times the average angular speed ofthe barrel during that interval. The difference between the averageangular speed of the sight line relative to the craft and the averageangular speed of the barrel relative to the craft is that is, l/(l-i-a)times the average angular speed of the barrel and in the oppositedirection. Through appropriate designing of the different gear wheels,it is achieved that this displacement of the glass plate 18 isproportional to the tracking movement of the barrel, but in a directionopposite the last-mentioned movement, and will also have an angularvelocity which is only 1 +0: of the angular velocity of the barrel. Inthis way, the glass plate 18 with its reticule is displaced in relationto the sight 10 in a direction opposite the movement of the barrel, andin this way the sight is given reduced angular velocity relative to thebarrel movement which is only 1 +0: of the speed of said movement. Thisdisplacement of the glass plate 18 with its reticule in relation to thesight 10 takes place only during the time (at-t which has n set, andafter said time the reticule and sight do not move relative to eachother, but both follow the rate of movement of the barrel exactly.

When the projectile has been fired with the lead desired, the positionof the reticule in relation to the sight can be set back again with theaid of the knobs 28 and 38.

The eifect of the displacements and movements described above areappropriately explained in more detail with the aid of the two diagramsin FIGS. 3 and 4. FIG. 3 shows the angular velocity u: in relation to afixed base for the target and the barrel and the reticule as a functionof the time T. The angular velocity to is plotted as ordinate, while thetime has been plotted as abcissa.

On the time axis, T is the time when the gunner, by depressing the pedal16, starts the timer 14, and T is the time when the timer interrupts theemission of current pulses at the end of the time interval axr The speedof the target m is assumed to be constant, and is indicated in FIG. 3 bythe straight double line 48. Up to the time point T it is assumed thatboth the barrel and the reticule move with the same angular velocity asthe target, and their movements will thus coincide with the line 48 upto the time T At the time point T as mentioned above, the reticuleobtains the extra component of movement in a direction opposite thetracking movement of the barrel, and this involves that the angularvelocity of the sight line in relation to the fixed base during the timeimmediately at the moment of time T will be somewhat lower than thespeed of the target, which is shown in FIG. 3 by means of the dashedline 49. However, the gunner will try to cause the reticule to followthe moving target, and the barrel will thereby have a higher angularvelocity than the target. The speed of the barrel is shown in FIG. 3 bythe heavy curve 50. At the time point T the gunner has managed to setthe reticule so that it coincides entirely with the position and speed(m of the target. At the time point T the barrel will thereby have aspeed corresponding to At the time point T the current through theelectromagnets 32 and 42 is switched off, and the displacement of theglass plate 18 with its reticule in relation to the sight ceases.Therefore, at the same time point (T the angular velocity of thereticule suddenly increases from m to As the gunner still tries tofollow the target with the reticule, after the time point T the speed ofthe reticule and thereby also the speed of the barrel will be decreasedto the speed m of the target, and will eventually coincide entirely withthis speed.

The way in which the variations shown in FIG. 3 as regards the angularvelocities of the reticule and the barrel will affect the angularpositions is shown in FIG. 4.

Here the angular position to in relation to a fixed base has beenplotted as ordinate and the time T as abscissa. As the speed of thetarget is assumed to be constant, its angular position will increaseuniformly during the whole of the time, and will follow the straightdouble line designated 51 in FIG. 4. Up to the time point T both thebarrel and the reticule have the same angular velocity as the target,and its angular positions will therefore follow the line 51 up to thistime. At said time point T the angular velocity of the reticule will bereduced to and this has the result that, immediately after the time Tthe reticule will assume angular positions which fall short of theangular positions of the target obtained for the corresponding times(according to the double line 51). These deviating angular positions areindicated in FIG. 4 by the dashed line 52. However, the gunner tries tomake the reticule coincide with the target as closely as possible, andthis has the result that the barrel is given an increased speed inrelation to the target, and after the time point T the angular positionof the barrel will be somewhat in excess of the corresponding angularpositions of the target (according to the double line 51) and theselarger angular positions in relation to the target are shown in FIG. 4by the curve 53, drawn with a heavy line. At the time point T (otX!after the time T the gunner has succeeded in making the angular positionof the reticule coincide with the angular position of the target, andduring the interval between the times T and T aXt both the reticule andthe target will have moved to the angle al Xw Between the times T and Tthe barrel constantly has an angular velocity which is times greaterthan that of the reticule, and this signifies that the angular positionof the barrel at the time T will be at X greater than the angularposition at the time T The differences between the angular position ofthe barrel and the angular position of the reticule and the target atthe time T will therefore amount to t Xw which is the correct lead thatit is desired to obtain. Immediately after the time T the reticule, asshown by FIG. 3, will have a greater speed than the speed of the target,which, however, can comparatively quickly be reduced by the gunner, sothat immediately after the time T the speed of the target and thereticule and the barrel will coincide. This is shown in FIG. 4 by theincreased angular position of the reticule (the dashed line 52A)immediately after the time T and a corresponding raising of the line 53.When the gunner has made the speeds of the reticule and the barrel withthe target movement, the angular position of the reticule will coincidewith that of the target, i.e. it will follow the double line 51, whilethe angular position of the barrel will be changed according to the partof the line 53 running parallel with the double line 51 at a distance oft Xw from same.

To summarize, it can thus be established that, by giving the reticule areduced speed relative to the barrel, which is only of the speed of thebarrel during the time interval T -T (=atXl and by the gunner trying tomake the reticule coincide with the target, immediately after the time Tthe desired lead of the barrel r td will be obtained automatically.

In the example described above, the extra component of movement of theline of sight in the direction opposite the tracking movement of thebarrel has been achieved by the reticule having been displaced inrelation to the sight. It would also be possible to have the whole ofthe sight move in the way intended in relation to the barrel. The timeinterval fixed nt-t can, of course, be obtained in some way other thanby means of a timer graduated for the range to the target. Thus, itwould be possible to obtain this time function directly from arange-finding instrument, the setting device of which could possibly bemechanically connected to the pointer of a timer. Furthermore, themovement of the reticule can be complemented in such a way that, beforetaking out the lead, the tangent elevation and the corrections desired,eg for the influence of the wind, powder, temperature etc., can be setwith the knobs 28 and 38. Furthermore, the two knobs 28 and 38 can bereplaced by motors, so that automatic resetting of the reticule isobtained, and these motors will effect the above-mentioned setting ofcorrections.

The present invention can also be used in cases when the trackingmovements of the barrel in relation to a fixed base cannot be registereddirectly. This is often the case, for instance, with track-layingvehicles with firearms in fixed mounting so that the aiming of the gunbarrel must be carried out through movements of the whole vehicle.

In such cases, the changes of the angular position of the barrel aremeasured continuously in relation to a gyroscope, during the fixedperiod of time axis, and at the same time, a servomechanism gives theline of sight an extra component of movement, which has a directionopposite the movement of the barrel in relation to the gyroscope and anangular velocity which is 1 +0: of the angular velocity of thelast-mentioned movement, whereby the movement of the line of sight inrelation to a fixed base will be reduced in relation to the movement ofthe barrel and is given an angular velocity which is only times theangular velocity of the barrel.

In the claims:

1. In a method of determining the correct lead re quired for firing aprojectile from a gun barrel at a moving target, the steps of:

initially moving the sight line and the gun barrel both at the sameangular velocity relative to the target until the sight line and thebarrel are aimed at the target;

then applying to the sight line an additional velocity componentangularly opposite to the concurrent movement of the barrel for aselected interval of time while moving the barrel and the sight line toaim the sight line at the target during said interval, said intervalbeing a constant at times the time of flight (t of the projectile fromthe barrel to the target, said additional oppositely directed velocitycomponent being such that the angular velocity of the line of sight is1+0: of the angular velocity of the barrel during said interval, a beinga constant; and

stopping at the end of said time interval the relative movement of thesight line and the gun barrel and continuing to aim the sight line atthe target at an angular velocity equal to that of the barrel.

2. In a method of determining the correct lead for firing a projectilefrom a gun barrel at a moving target, the steps of (a) initially movingthe sight line and the gun barrel both at the same angular velocityrelative to the target until the sight line is tracking the target andthe gun barrel is aimed at the target;

(b) then driving the sight line angularly and oppositely relative to thegun barrel at a constant 1+0: times the angular velocity of the barrelfor a predetermined interval of time at times the time t while seekingto continue tracking the target where a is a constant and t is the timeof flight of the projectile from the barrel to the target; and

(c) at the end of said time interval stopping the relative movement ofthe sight line and the gun barrel and continuing to aim the sight lineand the barrel at the target.

3. The method according to claim 2 wherein said constant a is selectedin accordance with the desired firing accuracy and the velocity of thetarget, the selected value being within the range of 0.5 and 3.

4. An apparatus for determining the correct lead for firing a projectilefrom a gun barrel at a moving target, said apparatus comprising incombination:

a gun barrel mounted to be elevated and traversed;

a sighting asembly including a carrier bearing a reticule, said carrierbeing movably mounted for vertical and transverse displacement of thereticule alternatively with or relative to the gun barrel;

transmission means coupled to said carrier for imparting to the same arelative movement proportional to and in opposition to the angularmovement of the gun barrel, said relative movement of the carrier withreference to the gun barrel reducing the angular velocity of the line ofsight in relation to that of the gun barrel by a factor JZL 1+ where ais a constant; and

actuating means adapted to be coupled to said transmission means andmeans operable to couple said actuating means for a set interval oftime, and to uncouple said actuating means at the end of said interval,the carrier then being free to be moved at the angular velocity of thegun barrel.

5. The apparatus according to claim 4 where said transmission means andactuating means comprise power drive means and gear means for displacingsaid carrier by said drive means to etfect vertical and transversedisplacement respectively of the carrier and thus of the reticule; andwherein said operable means comprise clutch means for coupling the gearmeans to the drive means, said clutch means biased into a disengagedposition, timer means connected to said clutch means to move the sameinto a position of engagement for said set time interval, and meansoperable to activate said timer means for the aforesaid purpose when theline of sight tracks the target and the gun barrel is aimed at thetarget.

References Cited UNITED STATES PATENTS 1,936,442 11/ 1933 Willard.

2,012,960 9/1935 Coupland.

2,356,189 8/1944 Tufts.

2,407,191 9/1946 Tear et al.

2,569,5 6O 10/ 1951 Ford.

2,690,014 9/1954 Draper et al.

ROBERT B. HULL, Primary Examiner

